Certification of a 41Ca dose material for use in human studies (IRMM-3703) and a corresponding set of isotope reference materials for 41Ca measurements (IRMM-3701)

The long-living radioisotope 41Ca could overcome current limitations in assessing the impact of interventions on bone health in controlled human studies. Changes in bone Ca metabolism can be identified directly via the induced changes in 41Ca excretion from 41Ca-labelled bones via the n(41Ca)/n(40Ca) ratio in urine. A 41Ca dose material (IRMM-3703), for use in human studies, was produced by IRMM within the EC funded project OSTEODIET. The 41Ca base material was purified and the purified solution is certified for both isotopic composition and amount content by isotope dilution mass spectrometry. The 44Ca-enriched isotope reference material, IM-6009, was used as spike and the natural Ca reference material, IM-6008, was used for correction of procedural bias. Isotope ratio measurements were performed using thermal ionisation mass spectrometry (TIMS). The certified n(41Ca)/n(40Ca) ratio in IRMM-3703 is 0.012789 (58). A set of synthetic isotope mixtures, IRMM-3701, was prepared from IRMM-3703. It enables comparability of 41Ca measurement results in different laboratories and by different techniques. The IRMM-3701 series is derived from gravimetric mixing of IRMM-3703 and a Ca solution of natural isotopic composition. It covers n(41Ca)/n(40Ca) ratios in the range of 1.0114(68) × 10−6 to 1.0524(71) × 10−13.